BOAC,
I'll probably get shot down in flames here - but I've a recollect that you need to set up a Guest account on the Host in order for the Client to get access as any network access is done as "Guest". Now, this may be flim-flam, but I did it and since I put the guest account on the host then every other client sees the shared drive & printers.
I would suggest taking a starting look
http://support.microsoft.com/kb/308007 which has links onward to the various troubleshooting areas including the Guest account checking.
Other than that, I agree with Background Noise that the firewalls may be worth checking, again a first principles check at each end.
Good luck with it